Treatment of dye aqueous solutions using a novel aromatic polyamide asymmetric nanofiltration membrane

ABS The textile industry produces enormous quantities of dye wastewater, containing high salt and organic concentrations, which are therefore difficult to be treated. In this work, an asymmetric Poly(m-phenylene isophthalamide) (PMIA) nanofiltration membrane was prepared by phase inversion method in order to reduce the quantity of the disposed water and, at the same time, to reuse the treated water. The morphology of the resulting membrane was characterized by scanning electron microscopy (SEM) as well as atomic force microscopy (AFM), and the molecular weight cut-off of the membrane was estimated using different polyethylene glycol (PEG) solutions. The asymmetric membrane was also evaluated for the removal of three different anionic dyes (acid, direct and reactive dyes). The effects of various parameters, such as pressure, pH, feed temperature and the presence of salt were evaluated. It was observed that the rejections of three dyes were all above 95% under 0.7 MPa at 25 °C. Long-term operating experiments showed that the membranes with a 900 Da cut-off could be used to concentrate 100 mg/L saline direct blue 71 solution with a high flux (> 50 L/m².h), a high dye rejection (>96%) and a salt retention lower than 6%. The newly developed nanofiltration membrane is suitable for the treatment of dye effluents.